Add Jupyter Chat Participant (@jupyter agent)

[Copilot]

Implements a VS Code Chat Participant (agent) for the Jupyter extension, enabling users to invoke @jupyter in the chat panel.

Changes

• package.json: Added chatParticipants contribution registering jupyter.jupyterAgent
• src/standalone/chat/agent.node.ts: New chat handler with basic capability response
• src/standalone/chat/extension.node.ts: Wired up agent registration during activation
• package.nls.json: Added localized description string

Usage

@jupyter How do I configure my notebook?

The agent responds with available capabilities: kernel configuration, package management, and kernel restart functionality.

Original prompt

Implement this.

The user has attached the following uncommitted or modified files as relevant context:
Untitled-1

agent: agent

What is 1+2
Untitled-1

Created from VS Code.

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.